You sound just like me last summer with my twin boyz. I had tried everything I could think of and had no results. What I ended up doing is giving them jelly beans. I hated rewarding with food but it was the only thing that worked. They got 1 if they went pee, 2 if they pooped and an extra jelly bean if they stayed dry. I think it also helped to havi them in the bathroom together. I would praise up a storm if one was "a big boy," and gave that one a lot of positive attention. If the other one started to speak out I'd remind him that his brother was a "big boy" and if he used the potty he would be a "big boy" too.
I realized early on that they were trying to keep wetting themselves in order to go back to pull-ups, when the realized they would be stuck in wet clothes and have to change themselves it wasn't fun anymore and they got better.
With the one I did have to have them "clean" their own underware when they pooped in them. He would have to wash them out in the shower and they had to clean themselves. It was a little on the mean side but they had to realize that they did have control but that it wasn't much fun when they had to do all the work.
Hope atleast some of this advise is helpfull. Good luck with your twins, They have their own added blessings and chalenges.
C.
Mom of 18 (3 biological (15 daycare)